(527c) Novel Assembly of Charge Mosaic Membranes for Salt Separation from Aqueous Solutions

Charge mosaic membranes are of interest for desalination as salt, the minor component, is preferentially transported instead of water. This contrasts to the selective transport of water, the major component, in reverse osmosis. The literature related to charge mosaic membranes is limited. Here, a novel method for assembly and use of charge mosaic structures is presented.

The method utilizes layer by layer deposition of an anionic and cationic polymers inside the pores of an ultrafiltration support. The sequential deposition of polyelectrolytes enables control over the thickness of the charge mosaic structure. Membranes were prepared using either poly(allylamine hydrochloride)/poly(styrene sodium sulfonate) or ε-poly-l-lysine hydrochloride/sodium alginate as counterion polyelectrolytes. EDS was used to confirm membrane formation.

To enhance salt transport in filtration, one of the polymers used to form the membrane was added to the feed solution to increase salt solubility in the membrane through Gibbs-Donnan equilibrium. Membranes were characterized for broad ranges of membrane formation conditions, feed salt compositions, and concentration of polymer added to the feed solution.

Salt concentrations in the filtrate could be increased by up to a factor of 9 over that of the feed. The enhancement (negative rejection) depended strongly on feed salt and added polymer concentration. The membranes proved stable over extended periods of operation.

The design of a process that removes salt using the membranes is discussed. After salt is preferentially removed in a first stage, a second ultrafiltration stage is required to yield the desalinated water and allow recycle of the added polymer to the first stage.